1. Field of the Invention
The present invention relates to a thermal printer which is suitable for performing printing on a recording paper by selectively generating heat from a plurality of heating elements of a thermal head based on print information.
2. Description of the Related Art
A conventional thermal printer 51 will now be described with reference to FIGS. 5 and 6, a cylindrical platen roller 52 is rotatably supported on a frame side which is not shown. Also, above the platen roller 52, a rectangular thermal head 53 composed of line heads capable of moving toward or away from (head up/down) the platen roller 52 is arranged.
The thermal head 53 is composed of a head substrate 53a which has a plurality of heating elements (not shown) formed on the bottom of the drawing, a head mount 53b on which the head substrate 53a is mounted, and a ribbon separation plate 53c. 
Also, the thermal head 53 is supported by a head supporting member 54 so as to be movable toward and away from the platen roller 52. The head supporting member 54 includes a first head supporting member 55 having first substantially U-shaped arm portions 55a that face each other, a second head supporting member 56 having second substantially U-shaped arm portions 55a that are formed outside and face the first arm portions 55a. 
The first head supporting member 55 is made of materials such as aluminum whose heat radiation performance is satisfactory, a flat plate head supporting portion 55b which also serves as a heat radiation plate is integrally formed at the ends of the first arm portions 55a. A heat radiation portion 55c is formed by protrusions extending from the head supporting portion 55b to increase the surface area of the first heat radiation portion 55c. 
Also, in the first head supporting member 55, both ends of the thermal head 53 in the longitudinal direction are mounted below the head supporting portion 55b, wherein heat generated during printing operation escapes from the heat radiation portion 55c via the head supporting portion 55b that also serves as a heat radiation plate.
Also, in the second head supporting member 56, outside ends of the second arm portions 56a are integrally formed by connecting to an urging portion 56b with screws. A coil spring 57 is arranged between the urging portion 56b and the head supporting portion 55b of the first head supporting member 55, wherein the thermal head 53 mounted in the head supporting portion 55b is elastically urged toward the platen roller 52.
Also, in the first head supporting member 55, a pair of stopper portions 55d is curved and folded in a nonlinear form to prevent a gap between the head supporting portion 55b and the urging portion 56b from increasing by the urging force of the coil spring 57.
Also, in the first head supporting member 55, an adjusting screw 58 capable of adjusting the warpage of the thermal head 53 is fixed to the center position of the head supporting portion 55b in the longitudinal direction.
Also, in the first head supporting member 55, a first supporting hole 55f which is elongated in the vertical direction in the drawing is formed at ends of the first substantially U-shaped arm portions 55a, and a second circular supporting hole 56c is formed at ends of the second arm portions 56a located outside the first supporting hole 55f. 
Also, in the second head supporting member 56, a rod-shared urging portion 56d is protrudingly formed of the second arm portions 56a. The urging portion 56d is designed to be engaged with an urging member (not shown) arranged at the frame side.
Also, in the head supporting member 54, the first and second supporting holes 55f and 56c are supported by a supporting shaft (not shown) formed at the frame side, and when being rotated downward by the urging means, the thermal head 53 is turned down and can be pressure-contacted to the platen roller 52 by the urging force of the coil spring 57.
Also, in the thermal head 53, the center portion in the longitudinal direction is bent downward, so as to prevent from being wrinkled an ink ribbon (not shown), which is pressure-contacted to the platen roller 52 by a recording paper when the printing operation is performed.
However, in the conventional thermal printer 51, because the adjusting screw 58 is supported by the head supporting portion 55b which also serves as a heat radiation plate, when the thermal head 53 is bent by tightening the adjusting screw 58, the center portion along the longitudinal direction of the head mount 53b is separated from the head supporting portion 55b and a gap 59 is formed therebetween.
Because of this, heat generated from the thermal head 53 during printing can not easily escape through the head supporting portion 55b which also serves as a heat radiation plate, resulting in the thermal head 53 heating up during the printing process, thus possibly deteriorating the quality of an image printed on a recording paper.
Also, in the first head supporting member 55, because the first arm portions 55a, the head supporting portion 55b and the heat radiation portion 55c are made of materials such as aluminum whose heat radiation performance is satisfactory, thus the cost increases.
Furthermore, the thickness of the head supporting portion 55b made of materials like aluminum must be thick because the thermal head 53 is bent by tightening the adjusting screw 58, which increases the cost.